ANNOUNCEMENTS Reminder- Exam #3 is one week from today (April 23 rd ) Review session: Wednesday, April 21 5:00pm

When is the next exam? 1. One week from today 2. Two weeks from today 3. Next Wednesday 4. May 14th

The rate law for an elementary step is given by the equation for that step Elementary StepMolecularityRate Equation A → productUnimolecularRate= k[A] A + B → productBiomolecularRate= k[A][B] A + A → productBimolecularRate= k[A] 2 2A + B → productTermolecularRate= k[A] 2 [B]

Example: Ozone depletion by CFC’s Cl + O 3 → ClO + O 2 ClO + O → Cl + O 2 Overall reaction: Intermediate? Catalyst?

How to determine if a proposed reaction mechanism is “reasonable” H 2 + 2ICl → 2HCl + I 2 Proposed mechanism 1: Step 1: H 2 + ICl → HI + HCl (slow) Step 2: ICl + HCl → HI + Cl 2 Sum Rate Step 1 Step 2 Overall Proposed mechanism 2: Step 1: H 2 + ICl → HCl + HI (slow) Step 2: HI+ ICl → HCl + I 2 Sum Rate Step 1 Step 2 Overall

Two mechanisms for determining mechanisms 1. Determine and interpret rate law 2. Isotopic Labeling

CHAPTER 15 EQUILIBRIA

Alcohols can be made from alkenes and alkenes can be made from alcohols Alkene → Alcohol Alcohol → Alkene Mechanism:

The principle of microscopic reversibility

What is the equilibrium expression for Fe 2 S 3 (s) 2 Fe 3+ (aq) + 3 S 2- (aq) 1. 1: 2. 2: 3. 3: 4. 4:

Manipulating Equilibrium Expressions : N 2 (g) + 3 H 2 (g)  2 NH 3 (g) K = =5.5 x 10 5 Reversing Reactions Multiplying by a Factor

Manipulating Equilibrium Expressions : Adding Reactions Cu(OH) 2 (s)  Cu 2+ (aq) + 2 OH - (aq) K 1 = 1.6x Cu 2+ (aq) + 4 NH 3 (aq)  Cu(NH 3 ) 4 2+ (aq)K 2 = 1.2 x Cu(OH) 2 (s) + 4 NH 3 (aq)  Cu(NH 3 ) 4 2+ (aq) + 2 OH - (aq)K = ?

Cu(NH 3 ) 4 2+ (aq)  Cu 2+ (aq) + 4 NH 3 (aq) K = 8.5 x If [Cu 2+ ] = 1.0 x 10 -6, [NH 3 ] = 1.0 x 10 -3, [Cu(NH 3 ) 4 2+ ], then … 1. It is at equilibrium 2. Reaction goes forwards 3. Reaction goes backwards

Equilibrium Calculations: Your Pathway to Happiness 1. Write the equilibrium expression 2. Determine Q 1.if Q = K, it’s at equilibrium 2.if Q < K, reactants go to form products 3.if Q > K, products go to form reactants 3. Call the amount reacting “x” 4. Solve for x in the equilibrium expression 5. Use x to determine equilibrium concentrations

Given these initial concentrations, what will the final concentrations be when equilibrium is reached?

K in terms of pressure: K p vs. K c K p = K c (RT)  n  n = change in numbers of moles of gas 2 NH 3 (g) N 2 (g) + 3 H 2 (g) K c = 5.8 x 10 5 K p =

LeChatelier’s Principle: Doing the math 1-Liter flask contains 0.50 mol butane and 1.25 mol isobutane (at equilibrium) mol butane are added. What happens, and what is the result?